Thursday, January 07, 2016

When we talk about the number of dengue, malaria, tuberculosis, MERS, or avian flu cases - or of any other disease - the understanding is that the numbers we have are almost certainly incomplete, and nearly always a major under count.

The list goes on. For every West Nile infection reported in the United States there are likely 100 that go unreported. And this is true for one of the most advanced public health systems in the world.

Imagine the disease data `gap' from countries where surveillance and reporting capabilities are far less robust or where the political will to report these types of findings is lacking. For many countries there is little `up side' to reporting diseases like MERS or avian flu, and so they simply look the other way.

The lack of reported MERS cases in sub-Saharan Africa, or relatively low numbers of human cases in bird flu endemic regions, yields far less reassurance when you consider those factors.

All of which brings us to a new report in the EID journal that takes retrospective look at the testing and diagnosis of suspected dengue cases in Brazil (where reporting is mandatory) over a 2 year period - and finds that even among those hospitalized and tested - the number of cases is badly under reported.

You can read the methods, materials, and math below, but the bottom line is they found that official counts likely captures less than 10% of the actual number of cases.

Since this study period, two new mosquito-borne viruses - Chikungunya and Zika - have been introduced into the region, have already likely produced millions of additional illnesses, and will further complicate the process of diagnosis and treatment going forward.

Volume 22, Number 2—February 2016

Letter

To the Editor: Dengue is an underreported disease globally. In 2010, the World Health Organization recorded 2.2 million dengue cases (1), but models projected that the number of symptomatic dengue cases might have been as high as 96 million (2). Brazil reports more cases of dengue than any other country (1);
however, the degree of dengue underreporting in Brazil is unknown. We
conducted a study to evaluate dengue underreporting by Brazil’s
Notifiable Diseases Information System (Sistema de Informação de Agravos
de Notificação [SINAN]).

From January 1, 2009, through December 31, 2011, we performed
enhanced surveillance for acute febrile illness (AFI) in a public
emergency unit in Salvador, Brazil. The surveillance team enrolled
outpatients >5 years of age with measured (>37.8°C)
or reported fever. Patients or their legal guardians provided written
consent. The study was approved by the Oswaldo Cruz Foundation Ethics
Committee, Brazil’s National Council for Ethics in Research, and the
Yale Institutional Review Board.

(BIG SNIP)

We estimated that overall, there were 12 dengue cases per reported
case in the community, but in months of low dengue transmission, this
ratio was >17:1 (Table). Comparable results have been observed in Nicaragua, Thailand, and Cambodia (6–8).
By applying the estimated multiplication factor to the study period’s
mean annual incidence of 303.8 reported dengue cases/100,000 Salvador
residents (9), we estimated that the actual mean annual dengue incidence for Salvador was 3,645.7 cases/100,000 residents.

We showed that dengue surveillance substantially underestimated
disease burden in Brazil, especially in what are considered
low-transmission periods. Dengue underreporting has been attributed to
passive case detection, which fails to identify persons with dengue who
do not seek health care (1). We also showed that surveillance failed to detect dengue cases among symptomatic patients seeking health care.

Novel surveillance tools, such as active syndromic surveillance and
point-of-care testing, should be applied to improve estimates of dengue
incidence. Furthermore, given the recent emergence of chikungunya and
Zika virus in Brazil (10), improved surveillance and laboratory diagnostics are needed to avert misclassification and mismanagement of cases.